Low heat loss and small contact area composite electrode for a phase change media memory device

ABSTRACT

A low heat loss and small contact area electrode structure for a phase change media memory device is disclosed. The memory device includes a composite electrode that includes a dielectric mandrel that is connected with a substrate and having a tapered shape that terminates at a vertex. An electrically conductive material conformally covers the dielectric mandrel and terminates at a tip. A first dielectric layer covers all of the composite electrode except an exposed portion of the composite electrode that is adjacent to the tip. A phase change media is in contact with the exposed portion. The exposed portion is only a small percentage of an overall surface area of the composite electrode so that a contact footprint between the exposed portion and the phase change media is small relative to a surface area of the phase change media and Joule heat transfer from the phase change media into the composite electrode is reduced.

FIELD OF THE INVENTION

[0001] The present invention relates generally to a composite electrodeincluding a low heat loss and small contact area interface with a phasechange media. More specifically, the present invention relates to aphase change media memory device in which a composite electrode includesan exposed portion in contact with the phase change media. The exposedportion comprises a small percentage of an overall area of the compositeelectrode such that there is a small area footprint between the exposedportion and the phase change media and the small area footprint reducesheat transfer from the phase change media to the composite electrode.

BACKGROUND OF THE ART

[0002] Memory storage devices based on a phase change material to storeinformation are being considered as an alternative to conventional datastorage devices such as hard discs and flash memory, just to name a few.In a phase change material based memory device, data is stored as one oftwo physical states of the phase change material.

[0003] For instance, in an amorphous state, the phase change materialcan represent a binary zero “0” and the state of the phase changematerial can be determined by passing a current through two electrodesin contact with the phase change material and sensing a voltage dropacross the phase change material. If in the amorphous state, the phasechange material has a high resistance, then the voltage drop will behigh.

[0004] Conversely, the state of the phase change material can be alteredto a crystalline state that represents a binary one “1” by passing acurrent of sufficient magnitude through the electrodes such that thephase change material undergoes Joule heating. The heating transformsthe phase change material from the amorphous state to the crystallinestate. As mentioned above, a voltage drop across the phase changematerial can be used to sense the state of the phase change material.Therefore, if in the crystalline state, the phase change material has alow resistance, then the voltage drop will be low.

[0005] Another way of expressing the state of the phase change materialis that in the amorphous state, the phase change material has a lowelectrical conductivity and in the crystalline state, the phase changematerial has a high electrical conductivity.

[0006] Ideally, there should be a large enough difference between thehigh resistance of the amorphous state and the low resistance of thecrystalline state to allow for accurate sensing of the state of thephase change material. Moreover, in a memory device based on an array ofphase change material storage cells, some of the storage cells will bein the amorphous state and others will be in the crystalline state. Itis desirable to have a minimal variation in the high resistance amongthe storage cells in the amorphous state and to have a minimal variationin the low resistance among the storage cells in the crystalline state.If either variation is too large, it may be difficult or impossible toaccurately sense the state of the phase change material.

[0007] In FIG. 1, a prior phase change storage cell 100 includes a firstelectrode 103, a second electrode 105, a dielectric 107, and a phasechange material 101 positioned in the dielectric 107 and in electricalcommunication with the first and second electrodes (103, 105).Typically, the dielectric 107 forms a chamber that surround the phasechange material 101. To alter the state of the phase change material 101from an amorphous state a (denoted by vertical hash lines) to acrystalline state C (see horizontal hash lines in FIG. 2), a current Iis passed through the first and second electrodes (103, 105). The flowof the current I through the phase change material 101 causes the phasechange material 101 to heat up due to Joule heating J.

[0008] In FIG. 2, a heat H generated by the current I is primarilydissipated through the first and second electrodes (103, 105) becausethe first and second electrodes (103, 105) are made from a materialhaving a high thermal conductivity, such as an electrically conductivemetal, for example. To a lesser extent, a heat h′ is dissipated throughthe dielectric 107 because the dielectric 107 has a lower thermalconductivity than the first and second electrodes (103, 105). Forinstance, the dielectric 107 can be a layer of silicon oxide (SiO₂).

[0009] As the heat H flows through the phase change material 101, aportion of the phase change material 101 undergoes crystallization to acrystalline state C (denoted by horizontal hash lines), while anotherportion of the phase change material 101 remains in the amorphous statea.

[0010] One disadvantage of the prior phase change storage cell 100 isthat not all of the energy contained in the Joule heat J is used intransforming the state of the phase change material 101 from theamorphous state a to the crystalline state C. Instead, a significantportion of the Joule heat J is wasted because it is thermally conductedaway from the phase change material 101 by the first and secondelectrodes (103, 105). As a result, more current I is required togenerate additional Joule heat J to overcome the heat loss through thefirst and second electrodes (103, 105).

[0011] Increasing the current I is undesirable for the followingreasons. First, an increase in the current I results in increased powerdissipation and it is desirable to reduce power dissipation inelectronic circuits. Second, an increase in the current I requireslarger driver circuits to supply the current I and larger circuitsconsume precious die area. In general, it is usually desirable toconserve die area so that more circuitry can be incorporated into anelectronic circuit. Finally, in battery operated devices, an increase inthe current I will result in a reduction in battery life. As portableelectronic devices comprise an increasingly larger segment of consumerelectronic sales, it is desirable to reduce current drain on batterypowered electronics so that battery life can be extended.

[0012] In FIG. 3, a plurality of the prior phase change storage cell 100are configured into an array to define a prior phase change memorydevice 111. Each storage cell 100 is positioned at an intersection ofthe first and second electrodes (103, 105), a plurality of which arearranged in rows for the second electrode 105 and columns for the firstelectrode 103.

[0013] In FIGS. 3 and 4, one disadvantage of the prior phase changememory device 111 is that during a write operation to a selected phasechange storage cell denoted as 100′, a substantial portion of the heat Hgenerated by the current I dissipates through the first and secondelectrodes (103, 105) and into adjacent phase change storage cells 100.Consequently, there is thermal cross-talk between adjacent storage cells100. Thermal cross-talk can slow down a switching speed of the phasechange memory device 111 and can cause the aforementioned variations inresistance among the storage cells 100.

[0014] Another disadvantage of the prior phase change memory device 111is that a surface of the phase change material 101 has a large contactarea C_(A) with the first and second electrodes (103, 105) (only thesecond electrode 105 is shown) and that large contact area C_(A)promotes heat transfer from the phase change material 101 into the firstand second electrodes (103, 105).

[0015] In FIGS. 3 and 4, the contact area C_(A) is the result of a largeportion of a surface area of the phase change material 101 being incontact with the first and second electrodes (103, 105) such that theheat H transfers easily from the phase change material 101 into theelectrodes. The large contact area C_(A) also contributes to theaforementioned thermal cross-talk. Moreover, heat loss from any givenstorage cell 100, thermal cross-talk from adjacent storage cells 100,and the contact area C_(A) acting individually or in combination canlead to wide variations in resistance among the storage cells 100. Forinstance, if one storage cell 100 has its phase change material 101preheated due to thermal cross-talk and another storage cell 100 doesnot have its phase change material 101 preheated, then when the phasechange material 101 of both cells undergoes Joule heating J, thepreheated cell 100 will have a greater percentage of its phase changematerial 101 crystallized than the non-preheated cell 100. Consequently,there may be variations in resistance between preheated andnon-preheated cells. As was mentioned previously, variations inresistance are undesirable.

[0016] Consequently, there exists a need for a conductor structure for aphase change media memory device that reduces transfer of Joule heatfrom the phase change media and that reduces the amount of currentnecessary to alter the state of the phase change media. There exists aneed for a conductor structure that reduces variations in resistanceamong phase change memory cells in a array. There is also need for aconductor structure that reduces thermal cross-talk and that reduces thesurface area of contact between a conductor and the phase change media.

SUMMARY OF THE INVENTION

[0017] The low heat loss and small contact area electrode structure ofthe present invention solves the aforementioned disadvantages andlimitations. The disadvantages associated with heat loss due to heattransfer into the electrodes is solved by a composite electrode thatincludes an exposed portion that is in contact with a phase changemedia. The exposed portion is only a small percentage of an overallsurface area of the composite electrode so that a contact footprintbetween the exposed portion and the phase change media is small relativeto a surface area of the phase change media. Consequently, only a smallarea of the phase change media is in contact with the exposed portion ofthe composite electrode and heat transfer into the composite electrodedue to Joule heating is reduced.

[0018] The disadvantages associated with increasing current tocompensate for heat loss through the electrodes is also solved by thecomposite electrode of the present invention because the exposed portionthereof presents a low thermal conductivity path to heat generated inthe phase change media.

[0019] Variations in resistance among cells of phase change media in anarray are reduced by the composite electrode of the present inventiondue to a low thermal cross-talk resulting from minimal heat transfer tothe composite electrode.

[0020] Additionally, the disadvantages associated with a large contactsurface area between the prior phase change material and its electrodesare solved by the contact footprint between the exposed portion of thecomposite emitter and the phase change media of the present invention.

[0021] Other aspects and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a cross-sectional view of a prior phase change storagecell.

[0023]FIG. 2 is a cross-sectional view of a prior phase change storagecell depicting Joule heat loss through a pair of electrodes.

[0024]FIG. 3 is a top plan view of a prior phase change memory device.

[0025]FIG. 4 is a cross-sectional view of heat loss through a priorphase change storage cell during a write operation.

[0026]FIG. 5A is a cross-sectional view of a low heat loss and smallcontact area electrode structure for a phase change media deviceaccording to the present invention.

[0027]FIGS. 5B and 5C are top plan views of a composite electrode havinga conical shape and a pyramid shape respectively according to thepresent invention.

[0028]FIG. 5D is a cross-sectional view of a write operation to a phasechange media device according to the present invention.

[0029]FIG. 5E is a top plan view taken along line AA of FIG. 5Ddepicting a contact footprint according to the present invention.

[0030]FIG. 5F is a cross-sectional view of thermal transfer of heat froma phase change media to a composite electrode according to the presentinvention.

[0031]FIG. 5G is a top plan view of a relationship between an overallsurface area of a composite emitter and a surface area of an exposedportion thereof according to the present invention.

[0032]FIGS. 6 and 7 are cross-sectional views of a low heat loss andsmall contact area electrode structure for a phase change media deviceaccording to the present invention.

[0033]FIGS. 8A through 8R depict a method of making a low heat loss andsmall contact area electrode structure for a phase change media deviceaccording to the present invention.

[0034]FIG. 9 is a top plan view of a phase change media memory accordingto the present invention.

[0035]FIGS. 10A, 10B, 11A, and 11B are profile views of possible shapesfor a composite electrode according to the present invention.

DETAILED DESCRIPTION

[0036] In the following detailed description and in the several figuresof the drawings, like elements are identified with like referencenumerals.

[0037] As shown in the drawings for purpose of illustration, the presentinvention is embodied in a low heat loss and small contact areaelectrode structure for a phase change media memory device and a methodof fabricating the same.

[0038] The low heat loss and small contact area electrode structure fora phase change media memory device includes a substrate and a compositeelectrode that includes a dielectric mandrel that is connected with thesubstrate and having a tapered shape that terminates at a vertex. Anelectrically conductive material conformally covers the dielectricmandrel and terminates at a tip. A first dielectric layer covers all ofthe composite electrode save an exposed portion of the compositeelectrode that is adjacent to the tip. A phase change media is connectedwith the first dielectric layer and the exposed portion of the compositeelectrode. A second dielectric layer is in contact with the firstdielectric layer and the phase change media. An electrode is in contactwith the phase change media.

[0039] The exposed portion is only a small percentage of an overallsurface area of the composite electrode so that a contact footprintbetween the exposed portion and the phase change media is small relativeto a surface area of the phase change media. By passing a currentbetween the electrode and the composite electrode, the phase changemedia undergoes Joule heating in a region proximate the contactfootprint between the exposed portion and the phase change media.Because only a small portion of the composite electrode and the phasechange media are in contact with each other, heat transfer from thephase change media into the composite electrode is reduced.

[0040] The reduced contact area between the composite electrode and thephase change media addresses the aforementioned disadvantages of theprior electrode structures. First, only a small percentage of thecomposite electrode is in contact with the phase change media.Therefore, heat loss and thermal cross-talk are reduced. Second, becauseheat loss is reduced, a magnitude of a write current necessary tocrystallize the phase change media can also be reduced. Fourth, thecontact footprint between the exposed portion and the phase change mediaaddress the problems associated with a large surface area of the priorphase change material being in contact with the prior electrodes.Finally, the reduced heat loss and thermal cross-talk minimizevariations in resistance.

[0041] In FIG. 5A, a low heat loss and small contact area electrodestructure for a phase change media memory device 10 includes a substrate11, a composite electrode 12 that includes a dielectric mandrel 13 thatis in contact with the substrate 11. The dielectric mandrel 13 has atapered shape that terminates at a vertex V. That is, the dielectricmandrel 13 is broad at a base B and is very narrow at the vertex V (seeFIG. 8F). The composite electrode 12 further includes an electricallyconductive material 15 that conformally covers the dielectric mandrel 13and terminates at a tip T. Because the electrically conductive material15 conformally covers the dielectric mandrel 13, the electricallyconductive material 15 has a shape that complements the shape of thedielectric mandrel 13. Therefore, the composite electrode 12 is broad atthe substrate 11 and narrow at the tip T.

[0042] A first dielectric layer 17 completely covers the compositeelectrode 12 except for an exposed portion E that is adjacent to the tipT. Therefore, a substantial portion of a surface area of theelectrically conductive material 15 is covered by the first dielectriclayer 17 and a small portion of the electrically conductive material 15(i.e. the exposed portion E) is not covered by the first dielectriclayer 17. For example, if the electrically conductive material 15 has athickness of about 2000 Å, then the exposed portion E may extend outwardof the first dielectric layer 17 by a distance of about 200 Å. A phasechange media 19 is in contact with the first dielectric layer 17 and theexposed portion E. A second dielectric layer 21 is in contact with thefirst dielectric layer 17 and the phase change media 19. An electrode 23is in contact with the phase change media 19.

[0043] Alternatively, the electrode 23 can be in contact with the phasechange media 19 and the second dielectric layer 21. In FIG. 6, thesecond dielectric layer 21 can include a via 26 therein that extends tothe first dielectric layer 17. The phase change media 19 can bepositioned in the via 26 with the electrode 23 also positioned in thevia 26 and in contact with both the phase change media 19 and the seconddielectric layer 21. In FIG. 7, an interconnect structure including athird dielectric layer 25 includes a via 28 therein that extends to thesecond dielectric layer 21. The electrode 23 is positioned in the via 28and is in contact with the phase change media 19.

[0044] The electrode 23 and the composite electrode 12 are operative toform an electrically conductive path through the phase change media 19.The electrodes (12, 23) can be in electrical communication with acurrent source (not shown). Passing a current through the electrodes(12, 23) generates Joule heating within the phase change media 19 and aportion of the phase change media 19 changes from an amorphous state toa crystalline state as will be described below.

[0045] As previously mentioned, the dielectric mandrel 13 has a taperedshape that is broad B at the substrate 11 and tapers to the vertex V.The composite electrode 12 has a shape that complements the shape of thedielectric mandrel 13. In FIGS. 5B and 10A, the composite electrode 12is depicted in isolation to better illustrate its shape. The compositeelectrode 12 can have a shape that includes but is not limited to a coneshape. In FIGS. 5B and 10A, the composite electrode 12 tapers from thebroad base B to the tip T such that the electrically conductive material15 has a sloping surface S. In the top plan view of FIG. 5B and theprofile view of FIG. 10A, the overall surface area of the electricallyconductive material 15 is substantially larger than the area of theexposed portion E.

[0046] Similarly, in FIG. 5C and FIG. 10B, the composite electrode 12can have a shape that includes but is not limited to a pyramid shape.The composite electrode 12 tapers from the broad base B to the tip T andthe electrically conductive surface 15 has a sloping surface S. In thetop plan view of FIG. 5C, each side of the pyramid (four are shown)slopes upward to the tip T. As mentioned above, in FIGS. 5C and 10B, theoverall surface area of the electrically conductive material 15 issubstantially larger than the area of the exposed portion E.

[0047] The pyramid and cone shapes of FIGS. 5B, 5C, 10A, and 10B neednot terminate at a sharp tip T, and the composite electrode 12 can havea shape that includes but is not limited a frustum of a cone as depictedin FIG. 11A wherein the composite electrode 12 tapers to a frustum tipT_(F). On the other hand, the composite electrode 12 can have a shapethat includes but is not limited a frustum of a pyramid as depicted inFIG. 11B wherein the composite electrode 12 tapers to a frustum tipT_(F). In FIGS. 5B, 5C, 10A, 10B, 11A, and 11B, the exposed portion E isa small percentage of the overall surface area of the electricallyconductive material 15 of the composite electrode 12.

[0048] The electrically conductive material 15 and the electrode 23 canbe made from a material including but not limited to those set forth inTABLE 1 below. Moreover, alloys of the materials set forth in TABLE 1below can also be used for the electrically conductive material 15 andthe electrode 23. TABLE 1 Materials for the electrically conductivematerial 15 and the electrode 23 A Metal Aluminum (Al) Tungsten (W)Molybdenum (Mo) Titanium (Ti) Copper (Cu)

[0049] The second dielectric layer 21 and the third dielectric layer 25can be made from a material including but not limited to those set forthin TABLE 2 below. TABLE 2 Materials for the second dielectric layer 21and the third dielectric layer 25 Silicon Oxide (SiO₂) Silicon Nitride(Si₃N₄)

[0050] The first dielectric layer 17 can be made from a materialincluding but not limited to those set forth in TABLE 3 below. TABLE 3Materials for the first dielectric layer 17 Tetraethylorthosilicate(TEOS) A Boron (B) doped Tetraethylorthosilicate (BSG) A Phosphorus (P)doped Tetraethylorthosilicate (PSG) A Boron (B) and Phosphorus (P) dopedTetraethylorthosilicate (BPSG) Silicon Oxide (SiO₂)

[0051] The dielectric mandrel 13 can be a dielectric layer that isconnected with the substrate 11 (see reference numeral 13 a in FIG. 8A).For instance, the dielectric layer 13 a can be connected with thesubstrate 11 by a method such as depositing, growing, or sputtering. Forexample, the dielectric layer 13 a can be a layer of silicon oxide(SiO₂) that is deposited on the substrate 11. The substrate 11 can be asemiconductor substrate such as silicon (Si), for example. As anotherexample, the substrate 11 can be a silicon substrate and the dielectriclayer 13 a can be formed by oxidizing a surface of the silicon substrateto form a layer of silicon oxide (SiO₂). Alternatively, the dielectriclayer 13 a can be a layer of glass, such as PYREX™, that is deposited onthe substrate 11.

[0052] In FIG. 5D, a write current i_(W), flowing through the electrodes(12, 23) and the phase change media 19 generates Joule heating withinthe phase change media 19. As the phase change media 19 heats up due tothe Joule heating, a portion of the phase change media 19 is transformedfrom an amorphous state to a crystalline state 19′. In FIG. 5D, theamorphous state is denoted as 19 and the crystalline state is denoted as19′. The Joule heating of the phase change media 19 occurs in a regionproximate the exposed portion E.

[0053] One advantage of the present invention is that only a portion ofa volume of the phase change media 19 that surrounds the exposed portionE is transformed to the crystalline state 19′. The portion of the phasechange media 19 that is in the crystalline state 19′ allows forconsistency in a resistance of the phase change media as measured acrossthe electrodes (12, 23). Consequently, because a small volume of thephase change media 19 can be consistently crystallized by a givenmagnitude of the write current i_(W), variations in resistance areminimized. Another benefit of crystallizing only a small volume of thephase change media 19 is that power consumption is reduced because themagnitude of the write current i_(W), the duration of the write currenti_(W), or both can be reduced as the entirety of the phase change media19 need not be crystallized during the write operation.

[0054] In FIG. 5E, a cross-sectional view along dashed line AA of FIG.5D illustrates an area A_(C) of a contact footprint between the exposedportion E of the electrically conductive material 15 and the phasechange media 19. The phase change media 19 has a total cross-sectionalarea A_(M) (shown in dashed line). As is depicted in FIG. 5E,A_(C)<<A_(M), that is, the contact footprint area A_(C) is much lessthan the total cross-sectional area A_(M). Similarly, the portion of thephase change media 19 that undergoes a phase change to the crystallinestate 19′ has an area A_(P) that is also less than the totalcross-sectional area A_(M). Therefore, the primary effect of the Jouleheat on the phase change media 19 is to heat only a relatively smallvolume of the phase change media 19 surrounding the contact footprintarea A_(C).

[0055] In FIG. 5F, Joule heat, generated by the current i_(W) (notshown), is thermally transferred primarily into the phase change media19 as shown by the heavy dashed arrows J_(H). Due to the aforementionedcontact footprint area A_(C), only a small portion of the Joule heat isthermally transferred into the electrically conductive material 15 ofthe composite electrode 12 or the electrode 23 as shown by the lighterdashed arrows j_(h). Some of the Joule heat may also be thermallytransferred into the first and second dielectric layers (17, 21) asdepicted by dashed arrows j′_(h).

[0056] In FIG. 5G, the small portion of Joule heat j_(h) that thermallytransfers into the electrically conductive material 15 of the compositeelectrode 12 is due to the exposed portion E having an exposed areaA_(E) that is in thermal contact with the phase change media 19; whereasa substantially larger portion N of the electrically conductive material15 having an area A_(N) is not in direct contact with the phase changemedia 19. Accordingly, the surface area of the composite electrode 12that is available as a direct thermal conduction path for the phasechange media 19 is limited to the exposed area A_(E).

[0057] In FIG. 9, a plurality of the low heat loss and small contactarea electrode structure for a phase change media memory devices 10 ofthe present invention can be arranged in an array 50 wherein the memorydevices 10 are positioned along rows and columns of the array 50. InFIG. 9, the electrically conductive material 15 of the compositeelectrode 12 are arranged as row conductors and the electrodes 23 arearranged as column conductors.

[0058] On the other hand, the electrically conductive material 15 of thecomposite electrode 12 can be columns conductors and the electrodes 23can be row conductors. The memory devices 10 are positioned at anintersection of the electrodes (15, 23) and the phase change media 19 ofeach memory cell 10 is depicted as dashed outline. The phase changemedia 19′ of one of the memory cells 10 is selected for a writeoperation by passing the current i_(W) through the electrodes (15, 23)that cross that cell 10.

[0059] Another advantage of the low heat loss and small contact areaelectrode structure for a phase change media memory devices 10 of thepresent invention is that as the phase change media 19′ undergoes Jouleheating during the write operation, the reduced heat transfer into thecomposite electrode 12 and the electrode 23 reduces thermal cross-talkbetween adjacent memory cells 10 in the array 50.

[0060] In FIGS. 8A through 8Q, a method of fabricating a low heat lossand small contact area electrode structure for a phase change mediamemory device 10 is illustrated.

[0061] In FIG. 8A, a dielectric layer 13 a is carried by a substrate 11.A mask layer is deposited on the dielectric layer 13, islithographically patterned, and is then etched to define a mandrel mask31. The dielectric layer 13 a and the substrate 11 can be from thematerials that were described above. The mask layer 31 can be a layer ofphotoresist material, for example.

[0062] In FIG. 8B, the dielectric layer 13 a and the mandrel mask 31 aredry etched using an etch gas that includes a first etch gas for etchingthe dielectric layer 13 a and a second etch gas for etching the mandrelmask 31. A plasma etch system can be used to perform the dry etch andthe first etch gas can be introduced into the plasma etch system to etchthe dielectric layer 13 a and the second etch gas can be introduced intothe plasma etch system to etch the mandrel mask 31. For example, thefirst etch gas can include a fluorocarbon (CF_(x)) based gas and thesecond etch gas can include oxygen (O₂) to ash the photoresist of themandrel mask 31.

[0063] In FIGS. 8C through 8F, the dry etching is continued until themandrel mask 31 is entirely dissolved (i.e. is etched away) and untilthe dielectric layer 13 a includes a dielectric mandrel 13 having atapered shape that terminates at a vertex V. The dielectric mandrel 13has a broad base B, a sloping surface S, and tapers to the vertex V.

[0064] In FIG. 8G, an electrically conductive material 15 is conformallydeposited on the dielectric mandrel 13 to form a composite electrode 12.A process such as chemical vapor deposition (CVD) can be used toconformally deposit the electrically conductive material 15. Asmentioned above, the composite electrode 12 has a shape that complementsthe dielectric mandrel 13 and terminates at a tip T. The electricallyconductive material 15 can be made from materials including but notlimited to those set forth above in TABLE 1. For example, after theconformal deposition, the electrically conductive material 15 can bepatterned and then etched to define a row conductor or a columnconductor (see FIG. 9 where the electrically conductive material 15 is arow conductor) that electrically connects all of the compositeelectrodes 12 in a row or a column of the array 50.

[0065] In FIG. 8H, a first dielectric material 17 is deposited on thecomposite electrode 12 until the first dielectric material 17 covers theentire composite electrode 12 including the tip T. The first dielectriclayer 17 can be made from a material including but not limited to thoseset forth in TABLE 3 above. A process such as CVD, for example, can beused to deposit the first dielectric material 17.

[0066] In FIG. 8I, the first dielectric layer 17 is planarized to form asubstantially planar surface. A process such as chemical mechanicalplanarization (CMP) can be used to planarize the first dielectric layer17. Alternatively, a reflow process can be used to form a substantiallyplanar surface on the first dielectric layer 17. For the reflow process,the first dielectric layer 17 can comprise a silicate glass, includingthose set forth in TABLE 3 above. The first dielectric layer 17 isheated to above a reflow temperature of the glass (e.g. above 500° C.)to reflow the glass into a smooth and substantially planar surface. Theplanarization of the first dielectric layer 17 can be accomplished usingother planarization processes and the present invention is not limitedto the planarization processes described herein. For instance, a resistetchback planarization process can be used to planarize the firstdielectric layer 17.

[0067] In FIG. 8J, the first dielectric layer 17 is dry etched until thefirst dielectric layer 17 recedes below a predetermined distance fromthe tip T of the composite electrode 12 so that an exposed portion Eadjacent to the tip T is not covered by the first dielectric layer 17. Aplasma etch process can be used to dry etch the first dielectric layer17 and that process can be timed to remove a sufficient amount of thefirst dielectric layer 17 such that the exposed portion E extendsoutward of the first dielectric layer 17 as depicted in FIG. 8J. Thepredetermined distance from the tip T will be application dependent. Forinstance, the predetermined distance can be a distance of about 200 Åfrom the tip T to first dielectric layer 17. Alternatively, a via (notshown) can be etched in the first dielectric layer 17 to expose the tipT.

[0068] In FIG. 8K, a layer of phase change media 29 is deposited on thefirst dielectric layer 17 and the exposed portion E of the compositeelectrode 12. For example, a process such as CVD, sputtering, orevaporation can be used to deposit the layer of phase change media 29. Atypical material for the layer of phase change media 29 includes but isnot limited to a germanium-antimony-tellurium material, such asGe₂Sb₂Te₅, for example.

[0069] In FIGS. 8L and 8M, the layer of phase change media 29 ispatterned 33 and then etched to define an island of phase change media19 that is positioned over the composite electrode 12 and in contactwith the exposed portion E.

[0070] In FIG. 8N, a second dielectric layer 21 is deposited on thefirst dielectric layer 17 and the islands of phase change media 19. Thesecond dielectric layer 21 can be a material including but not limitedto those set forth in TABLE 2 above.

[0071] In FIGS. 8O and 8P, the second dielectric layer 21 is planarizedusing a process such as CMP, for example. Next, the second dielectriclayer 21 is patterned 37 and then etched to form vias 39 that extend tothe islands of phase change media 19. Preferably, a dry etch process,such as a plasma etch, is used to etch the second dielectric layer 21.

[0072] In FIG. 8Q, an electrically conductive material 43 is depositedon second dielectric layer 21 and the vias 39 so that the electricallyconductive material 43 is in contact with the islands of phase changemedia 19. A process such as CVD or sputtering can be used to deposit theelectrically conductive material 43.

[0073] In FIG. 8P, the electrically conductive material 43 is patterned(not shown) and then etched to define an electrode 23. The electrode 23may be in contact with the phase change media 19 and the seconddielectric layer 21 as illustrated in FIG. 8P, or as described above inreference to FIG. 7, the electrode 23 may be in contact with the phasechange media 19. As was mentioned above in reference to FIG. 9, theelectrode 23 can be patterned and then etched to define a row conductoror a column conductor (see FIG. 9 where the electrode 23 is a columnconductor) that electrically connects all of the electrodes 23 in a rowor a column of the array 50.

[0074] Prior to the depositing the mask layer 31, as illustrated in FIG.8A, the dielectric layer 13 a can be formed on the substrate 11. Thedielectric layer 13 a can be deposited on the substrate 11. For example,if the substrate 11 is a silicon (Si) substrate, the dielectric layer 13a can be a layer of silicon oxide (SiO₂) deposited on the substrate 11.

[0075] In contrast, the dielectric layer 13 a can be grown on thesubstrate 11 by oxidizing the substrate 11. For instance, if thesubstrate 11 is a silicon (Si) substrate, then a layer of silicon oxide(SiO₂) can grown on a surface of the substrate 11 by an oxidationprocess to form the dielectric layer 13 a.

[0076] An electrical connection with the electrode 23 or theelectrically conductive material 15 of the composite electrode 12 can beaccomplished using interconnect structures that are well understood inthe microelectronics processing art including patterning and etching avia (not shown) that extends to the electrode 23 or to the electricallyconductive material 15 of the composite electrode 12 and then depositingan electrically conductive layer that fills the via and is in contactwith the electrode 23 or to the electrically conductive material 15.

[0077] Although several embodiments of the present invention have beendisclosed and illustrated, the invention is not limited to the specificforms or arrangements of parts so described and illustrated. Theinvention is only limited by the claims.

What is claimed is:
 1. A low heat loss and small contact area electrodestructure for a phase change media memory device, comprising: asubstrate; a composite electrode including a dielectric mandrelconnected with the substrate and having a tapered shape terminating at avertex and an electrically conductive material conformally covering themandrel and terminating at a tip; a first dielectric layer covering allbut an exposed portion of the composite electrode that is adjacent tothe tip; a phase change media connected with the first dielectric layerand the exposed portion; a second dielectric layer connected with thefirst dielectric layer and the phase change media; and an electrode incontact with the phase change media.
 2. The low heat loss and smallcontact area electrode structure of claim 1, wherein the electrode isconnected with the phase change media and the second dielectric layer.3. The low heat loss and small contact area electrode structure of claim1, wherein the composite electrode has a shape selected from the groupconsisting of a pyramid, a frustum of a pyramid, a cone, and a frustumof a cone.
 4. The low heat loss and small contact area electrodestructure of claim 1, wherein the composite electrode and the electrodeare conductors selected from the group consisting of a row conductor anda column conductor respectively and a column conductor and a rowconductor respectively.
 5. The low heat loss and small contact areaelectrode structure of claim 1, wherein the dielectric mandrel comprisesa dielectric layer connected with the substrate.
 6. The low heat lossand small contact area electrode structure of claim 5, wherein thedielectric layer is a material selected from the group consisting of aglass, a silicon substrate including a layer of silicon oxide disposedthereon, and a silicon substrate having an oxidized surface.
 7. The lowheat loss and small contact area electrode structure of claim 1, whereinthe first dielectric layer is a material selected from the groupconsisting of silicon oxide, tetraethylorthosilicate, borosilicateglass, phosphosilicate glass, and borophosphosilicate glass.
 8. The lowheat loss and small contact area electrode structure of claim 1, whereinthe second dielectric layer is a material selected from the groupconsisting of silicon oxide and silicon nitride.
 9. The low heat lossand small contact area electrode structure of claim 1, wherein theelectrically conductive material is a material selected from the groupconsisting of a metal, aluminum, tungsten, molybdenum, titanium, andcopper.
 10. The low heat loss and small contact area electrode structureof claim 1, wherein the electrode is an electrically conductive materialselected from the group consisting of a metal, aluminum, tungsten,molybdenum, titanium, and copper.
 11. A method of fabricating a low heatloss and small contact area electrode structure for a phase change mediamemory device, comprising: depositing a mask layer on a dielectriclayer; patterning and then etching the mask layer to define a mandrelmask; dry etching the dielectric layer and the mandrel mask with an etchgas comprising a first etch gas for etching the dielectric layer and asecond etch gas for etching the mandrel mask; continuing the dry etchinguntil the mandrel mask is entirely dissolved and until the dielectriclayer comprises a dielectric mandrel having a tapered shape thatterminates at a vertex; conformally depositing an electricallyconductive material on the dielectric mandrel to form a compositeelectrode including a shape that complements the dielectric mandrel andterminates at a tip; depositing a first dielectric layer on thecomposite electrode until the first dielectric layer completely coversan entirety of the composite electrode including the tip; planarizingthe first dielectric layer; dry etching the first dielectric layer untilthe first dielectric layer recedes below a predetermined distance fromthe tip of the composite electrode so that an exposed portion of thecomposite electrode adjacent to tip is not covered by the firstdielectric layer; depositing a layer of phase change media on the firstdielectric layer and the exposed portion; patterning and then etchingthe layer of phase change media to define an island; depositing a seconddielectric layer on the first dielectric layer and the island;planarizing the second dielectric layer; patterning and then etching thesecond dielectric layer to form a via extending to the island;depositing an electrically conductive material on the second dielectriclayer and in the via so that the electrically conductive material is incontact with the island; and patterning and then etching theelectrically conductive material to define an electrode.
 12. The methodas set forth in claim 11, wherein the first etch gas comprises afluorocarbon and the second etch gas comprises oxygen.
 13. The method asset forth in claim 11, wherein the dielectric layer is a materialselected from the group consisting of a glass, a layer of silicon oxidedeposited on a silicon substrate, and an oxidized surface of a siliconsubstrate.
 14. The method as set forth in claim 11, wherein the firstdielectric material is a material selected from the group consisting ofsilicon oxide, tetraethylorthosilicate, borosilicate glass,phosphosilicate glass, and borophosphosilicate glass.
 15. The method asset forth in claim 11, wherein the second dielectric material is amaterial selected from the group consisting of silicon oxide and siliconnitride.
 16. The method as set forth in claim 11, wherein theelectrically conductive material is a material selected from the groupconsisting of a metal, aluminum, tungsten, molybdenum, titanium, andcopper.
 17. The method as set forth in claim 11, wherein the electrodeis an electrically conductive material selected from the groupconsisting of a metal, aluminum, tungsten, molybdenum, titanium, andcopper.
 18. The method as set forth in claim 11 and further comprisingforming the dielectric layer on a substrate prior to depositing the masklayer.
 19. The method as set forth in claim 18, wherein the forming stepcomprises depositing the dielectric layer on the substrate.
 20. Themethod as set forth in claim 19, wherein the substrate is silicon andthe dielectric layer is silicon oxide.
 21. The method as set forth inclaim 18, wherein the forming step comprises growing the dielectriclayer on the substrate by oxidizing the substrate.
 22. The method as setforth in claim 21, wherein the substrate is silicon and the dielectriclayer is silicon oxide.
 23. The method as set forth in claim 11 whereinthe planarizing of the first dielectric layer comprises a processselected from the group consisting of a chemical mechanicalplanarization process and a reflow process.